Load reduction assemblies for a gas turbine engine

ABSTRACT

A load reduction assembly includes an annular bearing cone configured to extend between a bearing assembly and a frame assembly and form a first load path therebetween. The load reduction assembly further includes an annular recoupler member configured to extend between the bearing assembly and the frame assembly and form a second load path therebetween. The second load path is parallel to the first load path. The recoupler member includes a shape memory alloy configured to change stiffness in response to a change in a stress condition, thereby regulating an imbalance condition of a rotor shaft coupled to the bearing assembly.

BACKGROUND

The field of the disclosure relates generally to gas turbine enginesand, more particularly, to load reduction assemblies for use in gasturbine engines.

Gas turbine engines typically include a rotor assembly, a compressor,and a turbine. The rotor assembly includes a fan that includes an arrayof fan blades extending radially outward from a fan hub coupled to arotor shaft. The rotor shaft transfers power and rotary motion from theturbine to the compressor and the fan and is supported axially with aplurality of bearing assemblies spaced axially along the rotor shaft.Additionally, the rotor assembly has an axis of rotation that passesthrough a rotor assembly center of gravity. Known bearing assembliesinclude rolling elements and a paired race, wherein the rolling elementsare supported within the paired race. The rotor assembly is typicallysupported on three bearing assemblies, one of which is a thrust bearingassembly and two of which are roller bearing assemblies. The thrustbearing assembly supports the rotor shaft and supports axial and radialmovement of the rotor shaft assembly. The remaining roller bearingassemblies support radial movement of the rotor shaft.

During operation of the engine, a fragment of a fan blade may becomeseparated from the remainder of the blades and the rotor assembly. Thisis typically known as a fan blade out or a blade-off (FBO) event.Accordingly, a substantial rotary unbalanced load may be induced withinthe rotor assembly that is carried substantially by the fan shaftbearings, the fan bearing supports, and the fan support frames.

To reduce the effects of imbalanced loads, at least some known enginesinclude support components for the fan rotor support system that aresized to provide additional strength for the fan support system.However, increasing the strength of the support components alsoincreases an overall weight of the engine and decreases an overallefficiency of the engine when the engine is operated without substantialrotor imbalances.

Other known engines include a bearing support that includes amechanically weakened section, or primary fuse, that decouples the fanrotor from the fan support system. During such events, the fan shaftseeks a new center of rotation that approximates that of its unbalancedcenter of gravity. This fuse section, in combination with a rotorclearance allowance, is referred to as a load reduction device (LRD).The LRD reduces the rotating dynamic loads to the fan support system.After the primary fuse fails, the pitching fan rotor often induces alarge moment to a next closest bearing. The next closest bearing isknown as the number two bearing position. The moment induced to thenumber two bearing induces high bending and stress loads to the fanrotor locally. To relieve the high bending stresses, the radial andpitching rotation stiffness of the number two bearing position are oftensoftened or released during the FBO.

After FBO, the fan is typically allowed to rotate, in a process calledwindmilling, such that drag induced by the engine is reduced. However,during windmilling the loads induced by the rotor assembly and carriedby the fan bearings are lower than during the FBO. As such, the LRDdesigned for FBO increases vibration within the engine duringwindmilling because stiffness of the number two bearing position isreleased.

BRIEF DESCRIPTION

In one embodiment, a load reduction assembly is provided. The loadreduction assembly includes an annular bearing cone configured to extendbetween a bearing assembly and a frame assembly and form a first loadpath therebetween. The load reduction assembly further includes anannular recoupler member configured to extend between the bearingassembly and the frame assembly and form a second load paththerebetween. The second load path is parallel to the first load path.The recoupler member includes a shape memory alloy configured to changestiffness in response to a change in a stress condition, therebyregulating an imbalance condition of a rotor shaft coupled to thebearing assembly.

In another embodiment, a load reduction assembly is provided. The loadreduction assembly including an annular cage configured to extendbetween a bearing assembly and a frame assembly and form a load paththerebetween, wherein the annular cage includes a plurality ofcircumferentially spaced openings defined therein. The annular cagecomprises a shape memory alloy configured to change stiffness inresponse to a change in a stress condition, thereby regulating animbalance condition of a rotor shaft coupled to the bearing assembly.The load reduction assembly also includes a plurality of strutscircumferentially spaced around said cage and within said annular cageopenings. The plurality of struts configured to form a parallel loadpath with said cage of said recoupler member.

In a further embodiment, a load reduction assembly is provided. The loadreduction assembly includes an annular bearing support configured toextend between a bearing assembly and a frame assembly and form a loadpath therebetween. The annular bearing support includes at least onefirst member formed from a first alloy, and a second member coupled tothe at least one first member. The second member is formed from a secondalloy. The second alloy includes a shape memory alloy configured tochange stiffness in response to a change in a stress condition, therebyregulating an imbalance condition of a rotor shaft coupled to thebearing assembly.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of an exemplary turbofanengine in accordance with an example embodiment of the presentdisclosure.

FIG. 2 is a perspective view of an exemplary load reduction assemblythat may be used with the turbofan engine shown in FIG. 1.

FIG. 3 is a cross-sectional view of the load reduction assembly shown inFIG. 2 taken along line 3-3.

FIG. 4 is a perspective view of another exemplary load reductionassembly that may be used with the turbofan engine shown in FIG. 1.

FIG. 5 is a cross-sectional view of a further exemplary load reductionassembly that may be used with the turbofan engine shown in FIG. 1.

FIG. 6 is a cross-sectional view of yet another exemplary load reductionassembly that may be used with the turbofan engine shown in FIG. 1.

FIG. 7 is a cross-sectional view of yet a further exemplary loadreduction assembly that may be used with the turbofan engine shown inFIG. 1.

FIG. 8 is an illustration for an exemplary stress-strain curve for ashape memory alloy that may be used with the load reduction assembliesshown in FIGS. 2-5.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems comprisingone or more embodiments of this disclosure. As such, the drawings arenot meant to include all conventional features known by those ofordinary skill in the art to be required for the practice of theembodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and claims, reference will be made to anumber of terms, which shall be defined to have the following meanings.

The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately,” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged; such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

As used herein, the terms “axial” and “axially” refer to directions andorientations that extend substantially parallel to a centerline of anengine. Moreover, the terms “radial” and “radially” refer to directionsand orientations that extend substantially perpendicular to thecenterline of the engine. In addition, as used herein, the terms“circumferential” and “circumferentially” refer to directions andorientations that extend arcuately about the centerline of the engine.

Embodiments of a load reduction assembly for a turbofan engine asdescribed herein provide an assembly that facilitates reducing a fanblade out load and a subsequent windmilling load transferred from abearing assembly to an engine frame. Specifically, in the exemplaryembodiments, the load reduction assembly includes a shape memory alloymember that is responsive to a change in a stress condition so as tochange stiffness thereof, thus regulating an imbalance condition of arotor shaft coupled to the bearing assembly. As such, during a highstress condition of the fan blade out, the load reduction assemblyreduces stiffness such that the rotor shaft mode is reduced, and duringa low stress condition of windmilling, the load reduction assemblyregains its stiffness such that vibration loads are reduced. By formingthe load reduction assembly from the shape memory alloy overall engineweight is reduced and fuel efficiency is increased.

FIG. 1 is a schematic cross-sectional view of gas turbine engine 100 inaccordance with an exemplary embodiment of the present disclosure. Inthe exemplary embodiment, gas turbine engine 100 is embodied in ahigh-bypass turbofan jet engine, referred to herein as “turbofanengine.” As shown in FIG. 1, turbofan engine 100 defines an axialdirection A (extending parallel to a longitudinal centerline 102provided for reference) and a radial direction R (extendingperpendicular to longitudinal centerline 102). In general, turbofanengine 100 includes a fan case assembly 104 and a core engine 106disposed downstream from fan case assembly 104.

Core engine 106 includes an engine case 108 that defines an annularinlet 110. Engine case 108 at least partially surrounds, in serial flowrelationship, a compressor section including a booster or low pressure(LP) compressor 112 and a high pressure (HP) compressor 114; an annularcombustion section 116; a turbine section including a high pressure (HP)turbine 118 and a low pressure (LP) turbine 120; and a jet exhaustnozzle section 122. A high pressure (HP) shaft or spool 124 drivinglyconnects HP turbine 118 to HP compressor 114. A low pressure (LP) shaftor spool 126 drivingly connects LP turbine 120 to LP compressor 112. Thecompressor section, combustion section 116, turbine section, and nozzlesection 122 together define an air flow path 128.

In the exemplary embodiment, a fan assembly 129 includes a fan 130having a plurality of fan blades 132 coupled to a disk 134 in a spacedapart manner. As depicted, fan blades 132 extend outwardly from disk 134generally along radial direction R. Fan blades 132 and disk 134 aretogether rotatable about longitudinal centerline 102 by LP shaft 126. LPshaft 126 is supported at by a plurality of bearing assemblies, forexample a number two bearing assembly 136 at a forward end of LP shaft126. Bearing assembly 136 is coupled to an engine frame 138 through aload reduction assembly 140 that will be discussed in further detailbelow.

Referring still to the exemplary embodiment of FIG. 1, disk 134 iscovered by a rotatable front hub 142 aerodynamically contoured topromote an airflow through plurality of fan blades 132. Additionally,fan case assembly 104 includes an annular fan casing or outer nacelle144 that circumferentially surrounds fan 130 and/or at least a portionof core engine 106. Nacelle 144 is supported relative to core engine 106by a plurality of circumferentially-spaced outlet guide vanes 146.Moreover, a downstream section 148 of nacelle 144 may extend over anouter portion of core engine 106 so as to define a bypass airflowpassage 150 therebetween.

During operation of turbofan engine 100, a volume of air 152 entersturbofan engine 100 through an associated inlet 154 of nacelle 144and/or fan case assembly 104. As volume of air 152 passes across fanblades 132, a first portion 156 of air 152, known as fan stream airflow, is directed or routed into bypass airflow passage 150 and a secondportion 158 of volume of air 152 is directed or routed into air flowpath 128, or more specifically into booster compressor 112. A ratiobetween first portion 156 and second portion 158 is commonly referred toas a bypass ratio. The pressure of second portion 158 is then increased,forming compressed air 160, as it is routed through booster compressor112 and HP compressor 114 and into combustion section 116, where it ismixed with fuel and burned to provide combustion gases 162.

Combustion gases 162 are routed through HP turbine 118 where a portionof thermal and/or kinetic energy from combustion gases 162 is extractedvia sequential stages of HP turbine stator vanes (not shown) that arecoupled to engine case 108 and HP turbine rotor blades (not shown) thatare coupled to HP shaft or spool 124, thus causing HP shaft or spool 124to rotate, which drives a rotation of HP compressor 114. Combustiongases 162 are then routed through LP turbine 120 where a second portionof thermal and kinetic energy is extracted from combustion gases 162 viasequential stages of LP turbine stator vanes (not shown) that arecoupled to engine case 108 and LP turbine rotor blades (not shown) thatare coupled to LP shaft or spool 126, which drives a rotation of LPshaft or spool 126 and booster compressor 112, and/or rotation of fan130.

Combustion gases 162 are subsequently routed 164 through jet exhaustnozzle section 122 of core engine 106 to provide propulsive thrust.Simultaneously, the pressure of first portion 156 is substantiallyincreased as first portion 156 is routed through bypass airflow passage150 before it is exhausted from a fan nozzle exhaust section 166 ofturbofan engine 100, also providing propulsive thrust. HP turbine 118,LP turbine 120, and jet exhaust nozzle section 122 at least partiallydefine a hot gas path 168 for routing combustion gases 162 through coreengine 106.

Turbofan engine 100 is depicted by way of example only, in otherexemplary embodiments, turbofan engine 100 may have any other suitableconfiguration including for example, a turboprop engine, a militarypurpose engine, and a marine or land-based aero-derivative engine.

FIG. 2 is a perspective view of an exemplary load reduction assembly 200that may be used with turbofan engine 100 (shown in FIG. 1.). FIG. 3 isa cross-sectional view of load reduction assembly 200 taken along line3-3. Referring to FIGS. 2 and 3, in the exemplary embodiment, loadreduction assembly 200 includes an annular bearing cone 202 and anannular recoupler member 204. Bearing cone 202 includes a radially outerflange 206, a radially middle section 208, and a radially inner race210. Extending axially between radially middle section 208 and radiallyinner race 210 is a radially inner member 212. Radially inner member 212includes at least one fuse 214 defined thereon. In alternativeembodiments, radially inner member 212 does not include fuses definedthereon. Extending axially between radially middle section 208 andradially outer flange 206 is a radially outer member 216. As such,bearing cone 202 is generally V-shaped. In alternative embodiments,bearing cone 202 has any other structure and/or shape that enablesbearing cone 202 to function as described herein. In the exemplaryembodiment, bearing cone 202 is coupled to a static frame assembly 218at radially outer flange 206 and is coupled to a bearing assembly 220 atradially inner race 210. In the exemplary embodiment, bearing assembly220 includes the number 2 bearing of turbofan engine 100.

Recoupler member 204 includes a radially outer flange 224 and a radiallyinner flange 226 with a support member 228 extending therebetween.Radially outer flange 224 is coupled to static frame assembly 218 andradially inner flange 226 is coupled to a radially inner flange 230extending from second radially inner race 210. Recoupler member 204 isformed from a shape memory alloy (SMA). SMA is an alloy, such as, butnot limited to, a Nickel-Titanium (NiTi) alloy, aNickel-Titanium-Hafnium alloy, a Nickel-Titanium-Palladium alloy, or aCopper-Aluminum-Nickel alloy, that changes crystalline structure, andthereby mechanical properties, when subjected to mechanical stresschanges. For example, SMA at a lower stress condition is has greaterstiffness, but when loaded with mechanical stress, SMA at a higherstress condition has lower stiffness and is more ductile. Specifically,the lower stress phase is known as an austenite phase that has a firstcrystalline structure that facilitates an increased stiffness. Whenstress is applied above a predetermined stress level, SMA changes phaseto a higher stress phase that is known as a martensite phase and has asecond crystalline structure. The martensite phase facilitates SMA to besubjected to large deformations and a decreased stiffness. Themartensite phase has a modulus of elasticity that is lower than theaustenitic phase. This phase change is a reversible process, and SMA maychange from the martensite phase to the austenitic phase and back againwhile recovering strain therein. SMA is discussed further below inreference to FIG. 8.

In the exemplary embodiment, recoupler member 204 is formed from aplurality of individual SMA segments 234. By using multiple SMA segments234 the stiffness response of recoupler member 204 may be fine-tuned.For example, a first SMA segment 236 is responsive to a change in afirst predetermined stress condition and a second SMA segment 238 isresponsive to a change in a second predetermined stress condition suchthat the first stress condition is substantially not equal to the secondstress condition. In alternative embodiments, recoupler member 204 isunitary and formed from a rolled sheet of SMA. In other embodiments,recoupler member 204 is formed from SMA and at least one of radiallyouter flange 224 and/or radially inner flange 226 may be formed fromanother alloy, for example steel, and coupled to recoupler member 204through a weld.

Load reduction assembly 200 further includes a plurality of radiallyouter bolts 240 that facilitate coupling both bearing cone radiallyouter flange 206 and recoupler member radially outer flange 224 to frameassembly 218. A plurality of radially inner bolts 242 facilitatecoupling bearing cone radially inner flange 230 and recoupler memberradially inner flange 226 together such that recoupler member 204 iscoupled to bearing assembly 220. In alternative embodiments, bearingcone 202 is individually coupled to frame assembly 218 and/or bearingassembly 220 through fusible bolts such that fuse 214 does not need tobe defined on radially inner member 212.

In the exemplary embodiment, bearing assembly 220 is located in a numbertwo bearing position. As such, bearing assembly 220 is a fan thrustbearing. In alternative embodiments, load reduction assembly 200 may beused for any rotor bearing assembly within turbofan engine 100.

During general operation of turbofan engine 100, load reduction assembly200 forms a load path 244 from bearing assembly 220 to frame assembly218. For example, load reduction assembly 200 includes a parallel loadpath that includes bearing cone 202 as a first load path and recouplermember 204 as a second load path 246. As such, loads from LP shaft 126(shown in FIG. 1) are induced in bearing assembly 220 and transferredthrough load reduction assembly 200 to frame assembly 218. The loadsinduced through load reduction assembly 200 during general engine 100operations are such that SMA is in its austenite phase and has a highermodulus of elasticity as illustrated in FIG. 6 and discussed furtherbelow. Additionally, the loads induced through bearing cone 202 are suchthat fuse 214 is not overcome.

When turbofan engine 100 experiences a fan blade-out (FBO) event,wherein a portion of fan blades 132 (shown in FIG. 1) are removed fromturbofan engine 100, an imbalanced load is generated by LP shaft 126(shown in FIG. 1). The imbalanced load induces a radial load on bearingassembly 220 that depends on a natural frequency mode of LP shaft 126.As the FBO load induced through load reduction assembly 200 increases,exceeding a predetermined load that facilitates overcoming and breakingfuse 214 such that first load path 244 through bearing cone 202 isremoved. As such, recoupler member 204 and second load path 246 is asole load path between bearing assembly 220 and frame assembly 218.Higher loads are then transferred through recoupler member 204 such thata predetermined stress condition is induced through SMA, and SMA changesits phase to the martensite phase. As such, SMA has a lower modulus ofelasticity and facilitates dropping the frequency mode of LP shaft 126thereby regulating the imbalance load from the FBO event and reducingthe load transferring to frame assembly 218. In alternative embodiments,bearing cone 202 does not have a fuse, however higher loads are stilltransferred through recoupler member 204 such that a predeterminedstress condition is induced and the stiffness of load reduction assembly200 is reduced to facilitate dropping the frequency mode of LP shaft126.

During a post FBO event, also known as windmilling, the remaining fanblades 132 and LP shaft 126 continue to rotate to reduce aerodynamicdrag of turbofan engine 100. However, during windmilling, the imbalancedload subsides and the rotation of LP shaft 126 is slower therebyreducing loads generated by LP shaft 126 and reducing the induced loadson bearing assembly 220. As such, the lower loads that are below thepredetermined load and stress conditions for the martensite phase aretransferred through recoupler member 204. Thus, SMA changes its phaseback to its austenite phase and regains its strain and increases itsmodulus of elasticity. As such, vibration from windmilling is reduced inturbofan engine 100.

FIG. 4 is a perspective view of another exemplary load reductionassembly 300 that may be used with turbofan engine 100 (shown in FIG.1). In the exemplary embodiment, load reduction assembly 300 includes anannular cage 302. Annular cage 302 includes a radially outer flange 304that facilitates coupling load reduction assembly 300 to frame assembly218 (shown in FIG. 3) and a radially inner flange 306 that facilitatescoupling load reduction assembly 300 to bearing cone radially innerflange 230 and bearing assembly 220 (both shown in FIG. 3). Extendingbetween radially outer flange 304 and radially inner flange 230 are aplurality of circumferentially spaced support members 308. As such, aplurality of openings 310 are defined within annular cage 302 thatextend from radially outer flange 304 to radially inner flange 306. Inthe exemplary embodiment, annular cage 302 is formed from shape memoryalloy (SMA) as discussed above.

Load reduction assembly 300 further includes a plurality of struts 312that are circumferentially spaced around annular cage 302 and positionedwithin each opening 310 respectively. Each strut 312 includes a firstflange 314 and an opposite second flange 316. First flange 314corresponds to radially outer flange 304 and second flange 316corresponds to radially inner flange 306. In the exemplary embodiment,radially outer flange 304 and first flange 314 are coupled to frameassembly 218 through a plurality of radially outer bolts (not shown).Radially inner flange 306 and second flange 316 are coupled to bearingcage radially inner flange 230 through a plurality of radially innerbolts (not shown). In the exemplary embodiment, each strut 312 is formfrom an alloy other than SMA, for example steel.

Similar to the embodiments described above, load reduction assembly 300forms a load path from bearing assembly 220 to frame assembly 218.Additionally, within load reduction assembly 300, the load istransferred through both annular cage 302 and each strut 312 inparallel. During the FBO event, bolts that couple each strut 312, arefuseable and their strength overcome due to the load transferredtherethrough, thereby forming annular cage 302 as the sole load path.Annular cage 302 thus facilitates reducing the imbalanced load from theFBO event and windmilling, and changes phase between the austenite phaseand the martensite phase. Additionally, by forming openings 310 withinannular cage 302, the weight of load reduction assembly 300 is reduced,and material costs are reduced.

FIG. 5 is a cross-sectional view of a further exemplary load reductionassembly 400 that may be used with turbofan engine 100 (shown in FIG.1). In the exemplary embodiment, load reduction assembly 400 includes anannular bearing support 402 that extends between bearing assembly 220and static frame assembly 218. Bearing support 402 includes a bearingmember 404 that couples to bearing assembly 220 at a radially inner race406. Opposing radially inner race 406, bearing member 404 includes aflange 408. Bearing support 402 further includes a frame member 410 thatis coupled to frame assembly 218 at a first flange 412 through aplurality of bolts 414. Opposing first flange 412, frame member 410includes a second flange 416. In the exemplary embodiment, bearingmember 404 and frame member 410 are formed from a first alloy such assteel.

Bearing support 402 further includes an insert member 418 coupledbetween bearing member 404 and frame member 410. Insert member 418includes a first flange 420 that corresponds to frame member flange 416and an opposite second flange 422 that corresponds to bearing memberflange 408. In the exemplary embodiment, insert member 418 is formedfrom shape memory alloy (SMA) as discussed above. In some embodiments,insert member 418 includes a plurality of circumferentially spacedopenings 424 defined therein. Openings 424 facilitate reducing theweight of load reduction assembly 400 and as well as reducing materialcosts.

In the exemplary embodiment, insert member 418 is coupled to framemember 410 through a plurality of bolts 426 that extend through bothflanges 416 and 420 respectively. Additionally, insert member 418 iscoupled to bearing member 404 through a plurality of bolts 428 thatextend through both flanges 422 and 408 respectively. In someembodiments, insert member 418 is coupled to both frame member 410 andbearing member 404 through a double bolt connection having a radiallyouter bolt row and a radially inner bolt row. In other embodiments,insert member 418 is coupled to both frame member 410 and bearing member404 through a welded connection. Additionally, in alternativeembodiments insert member 418 and bearing member 404 may be formed as asingle member with SMA such that bearing support 402 includes only twomembers and one connection joint, frame member 410 and bearing member404 including SMA. Similarly, insert member 418 and frame member 410 maybe formed as a single member with SMA such that bearing support 402include only two members and one connection joint, frame member 410including SMA and bearing member 404. Furthermore, in the exemplaryembodiment, insert member 418 is illustrated as generally Z-shaped,however, in alternative embodiments, insert member 418 may have anyother shape that enables bearing support 402 to function as describedherein.

Similar to the embodiments described above, bearing support 402 formsthe load path from bearing assembly 220 to frame assembly 218. As such,during turbofan engine operation, load from LP shaft 126 (shown inFIG. 1) is transferred through bearing member 404, insert member 418 inthe austenite phase, and frame member 410. During the FBO event, higherloads from LP shaft 126 are transferred through insert member 418 suchthat upon exceeding a predetermined load, a predetermined stresscondition is induced through SMA, such that SMA changes its phase to themartensite phase. As such, SMA has a lower modulus of elasticity andfacilitates dropping the frequency mode of LP shaft 126, therebyregulating the imbalance load from the FBO event and reducing the loadtransferring to frame assembly 218. During windmilling, the rotation ofLP shaft 126 is slower, thereby reducing loads generated by LP shaft 126and reducing the induced loads on bearing assembly 220. As such, thelower loads that are below the predetermined load and stress conditionsfor the martensite phase are transferred through insert member 418.Thus, SMA changes its phase back to its austenite phase and regains itsstrain and increases its modulus of elasticity. As such, vibration fromwindmilling is reduced in turbofan engine 100. By forming only a portionof bearing support 402 with SMA, the weight of load reduction assembly400 is reduced, and material costs are reduced.

FIG. 6 is a cross-sectional view of yet another exemplary load reductionassembly 500 that may be used with turbofan engine 100 (shown in FIG.1). In the exemplary embodiment, load reduction assembly 500 includes anannular bearing support 502 that extends between bearing assembly 220and static frame assembly 218. Bearing support 502 includes a bearingmember 504 that couples to bearing assembly 220. Bearing support 502also includes a frame member 506 that is coupled to frame assembly 218through a plurality of bolts 508. In the exemplary embodiment, bearingmember 504 is formed from a first alloy such as steel and frame member506 from a second alloy such as a shape memory alloy (SMA) as discussedabove. Bearing member 504 and frame member 506 are coupled through aplurality of bolts 510. In alternative embodiments, frame member 506 maybe welded to both static frame assembly 218 and bearing member 504.

Similar to the embodiments described above, bearing support 502 formsthe load path from bearing assembly 220 to frame assembly 218. As such,during turbofan engine operation, load from LP shaft 126 (shown inFIG. 1) is transferred through bearing member 504 and frame member 506in the austenite phase. During the FBO event, higher loads from LP shaft126 are transferred through frame member 506 such that upon exceeding apredetermined load, a predetermined stress condition is induced throughSMA, such that SMA changes its phase to the martensite phase. As such,SMA has a lower modulus of elasticity and facilitates dropping thefrequency mode of LP shaft 126, thereby regulating the imbalance loadfrom the FBO event and reducing the load transferring to frame assembly218. During windmilling, the rotation of LP shaft 126 is slower, therebyreducing loads generated by LP shaft 126 and reducing the induced loadson bearing assembly 220. As such, the lower loads that are below thepredetermined load and stress conditions for the martensite phase aretransferred through frame member 506. Thus, SMA changes its phase backto its austenite phase and regains its strain and increases its modulusof elasticity. As such, vibration from windmilling is reduced inturbofan engine 100. By forming only a portion of bearing support 502with SMA, the weight of load reduction assembly 500 is reduced, andmaterial costs are reduced.

FIG. 7 is a cross-sectional view of yet a further exemplary loadreduction assembly 600 that may be used with the turbofan engine 100(shown in FIG. 1). In the exemplary embodiment, load reduction assembly600 includes an annular bearing support 602 that extends between bearingassembly 220 and static frame assembly 218. Bearing support 602 iscoupled to static frame assembly 218 through a plurality of bolts 508.In alternative embodiments, bearing support 602 may be welded to staticframe assembly 218. Bearing support 602 is formed from a shape memoryalloy (SMA) as discussed above.

Similar to the embodiments described above, bearing support 602 formsthe load path from bearing assembly 220 to frame assembly 218. As such,during turbofan engine operation, load from LP shaft 126 (shown inFIG. 1) is transferred through bearing support 602 in the austenitephase. During the FBO event, higher loads from LP shaft 126 aretransferred through bearing support 602 such that upon exceeding apredetermined load, a predetermined stress condition is induced throughSMA, such that SMA changes its phase to the martensite phase. As such,SMA has a lower modulus of elasticity and facilitates dropping thefrequency mode of LP shaft 126, thereby regulating the imbalance loadfrom the FBO event and reducing the load transferring to frame assembly218. During windmilling, the rotation of LP shaft 126 is slower, therebyreducing loads generated by LP shaft 126 and reducing the induced loadson bearing assembly 220. As such, the lower loads that are below thepredetermined load and stress conditions for the martensite phase aretransferred through bearing support 602. Thus, SMA changes its phaseback to its austenite phase and regains its strain and increases itsmodulus of elasticity. As such, vibration from windmilling is reduced inturbofan engine 100.

FIG. 8 is an illustration for an exemplary stress-strain curve 700 for ashape memory alloy that may be used with load reduction assemblies 200,300, 400, 500, and 600 (shown in FIGS. 2-7). In the exemplarystress-strain curve 700, x-axis 702 defines strain of SMA and y-axis 704defines stress of SMA. At a first load threshold (defined by points Aand B), SMA may undergo a large strain (e.g., for NiTi, typically in therange of 2% to 4%), thereby reducing stiffness and facilitatingdeformation of SMA. In this regard, point A represents the start of thesolid-solid phase transformation from austenite to martensite, and pointB represents the end of this solid-solid phase transformation.Additionally, SMA may recover all the strain once the load drops below asecond load threshold (defined by points C and D), thereby increasingstiffness and facilitating a return back to an initial shape. In thisregard, point C represents the start of the reverse phase transformationfrom martensite to austenite, and point D represents the end of thisreverse phase transformation.

The above-described embodiments of a load reduction assembly for aturbofan engine provides a cost effective method for reducing a fanblade out load and a subsequent windmilling load transferred from abearing assembly to an engine frame. During the fan blade out, a rotorshaft induces an imbalanced load on the bearing assembly. As such, theload reduction assembly reduces stiffness to reduce the rotor shaft modeand reduced the imbalanced load transferred to the engine frame.However, the imbalanced load subsides during windmilling. As such, theload reduction assembly increases stiffness to reduce vibrationtransferred to the engine frame. In the exemplary embodiments, the loadreduction assembly includes a shape memory alloy member that isresponsive to a change in a stress condition so as to change stiffnessthereof, thus regulating an imbalance condition of a rotor shaft coupledto the bearing assembly. Specifically, during a high stress condition ofthe fan blade out, the load reduction assembly reduces stiffness suchthat the rotor shaft mode is reduced, and during a low stress conditionof windmilling, the load reduction assembly regains its stiffness suchthat vibration loads are reduced. By forming the load reductionassemblies from the shape memory alloy both fan blade out loads andwindmilling loads are managed. The load reduction assembly thus reducesoverall engine weight and increases fuel efficiency.

Exemplary embodiments of methods, systems, and apparatus for loadreduction assemblies are not limited to the specific embodimentsdescribed herein, but rather, components of the systems and/or steps ofthe methods may be utilized independently and separately from othercomponents and/or steps described herein. For example, the methods mayalso be used in combination with other systems requiring load reductionsand the associated methods, and are not limited to practice with onlythe systems and methods as described herein. Rather, the exemplaryembodiment can be implemented and utilized in connection with many otherapplications, equipment, and systems that may benefit from loadreduction assemblies.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. A load reduction assembly comprising: an annularbearing cone configured to extend between a bearing assembly and a frameassembly and form a first load path therebetween; an annular recouplermember configured to extend between the bearing assembly and the frameassembly and form a second load path therebetween, the second load pathparallel to the first load path, wherein said recoupler member comprisesa shape memory alloy configured to change stiffness in response to achange in a stress condition, thereby regulating an imbalance conditionof a rotor shaft coupled to the bearing assembly; and wherein saidbearing cone comprises a fuse configured to be overcome during theimbalance condition of the rotor shaft such that said recoupler memberand the second load path is a sole load path between the bearingassembly and the frame assembly.
 2. The load reduction assembly of claim1, wherein said shape memory alloy is configured to have a firststiffness in response to a first predetermined stress sensed thereon. 3.The load reduction assembly of claim 1, wherein said shape memory alloyis configured to have a second stiffness in response to a secondpredetermined stress sensed thereon.
 4. The load reduction assembly ofclaim 1, wherein said shape memory alloy is configured to substantiallyregain an original stiffness after the imbalance condition subsides. 5.The load reduction assembly of claim 1, wherein said recoupler member isunitary.
 6. The load reduction assembly of claim 1, wherein saidrecoupler member further comprises at least one flange welded thereon.7. A load reduction assembly comprising: an annular bearing coneconfigured to extend between a bearing assembly and a frame assembly andform a first load path therebetween; and an annular recoupler memberconfigured to extend between the bearing assembly and the frame assemblyand form a second load path therebetween, the second load path parallelto the first load path, wherein said recoupler member comprises aplurality of shape memory alloy segments configured to change stiffnessin response to a change in a stress condition, thereby regulating animbalance condition of a rotor shaft coupled to the bearing assembly;and wherein a first shape memory alloy segment of said plurality ofshape memory alloy segments is responsive to a change in a first stresscondition and a second shape memory alloy segment of said plurality ofshape memory alloy segments is responsive to a change in a second stresscondition, the first stress condition is substantially not equal to thesecond stress condition.
 8. The load reduction assembly of claim 7,wherein at least one of said plurality of shape memory alloy segments isconfigured to have a first stiffness in response to a firstpredetermined stress sensed thereon.
 9. The load reduction assembly ofclaim 7, wherein at least one of said plurality of shape memory alloysegments is configured to have a second stiffness in response to asecond predetermined stress sensed thereon.
 10. The load reductionassembly of claim 7, wherein said plurality shape memory alloy segmentsare configured to substantially regain an original stiffness after theimbalance condition subsides.
 11. The load reduction assembly of claim7, wherein said recoupler member further comprises at least one flangewelded thereon.